code: def hybrid_forward(self, F, x_sub1, x_sub2, x_sub4):
      outputs = []
  
      x_cff_24, x_24_cls = self.cff_24(x_sub4, x_sub2)
      outputs.append(x_24_cls)
      x_cff_12, x_12_cls = self.cff_12(x_cff_24, x_sub1)
      outputs.append(x_12_cls)
  
      up_x2 = F.contrib.BilinearResize2D(
          x_cff_12,
          height=self._up_kwargs["height"] // 4,
          width=self._up_kwargs["width"] // 4,
      )
      up_x2 = self.conv_cls(up_x2)
      outputs.append(up_x2)
  
      up_x8 = F.contrib.BilinearResize2D(
          up_x2,
          height=self._up_kwargs["height"],
          width=self._up_kwargs["width"],
      )
      outputs.append(up_x8)
  
      # 1 -> 1/4 -> 1/8 -> 1/16
      outputs.reverse()
      return tuple(outputs)
  
imports: from __future__ import division
  from mxnet.gluon import nn
  from mxnet.context import cpu
  from mxnet.gluon.nn import HybridBlock
  from gluoncv.model_zoo.segbase import SegBaseModel
  from gluoncv.model_zoo.pspnet import _PSPHead
label_desc: Use image node_id 2 for calling the _ICHead obj's underlying member method code with example usage: obj.hybrid_forward(F, x_sub1, x_sub2, x_sub4) and returns: tuple